Fibers made of polyethylene terephthalate or a polyester comprising polyethylene terephthalate as a main component have a high melting point, a high modulus of elasticity, excellent heat resistance and chemical resistance. Thus, they are widely used in curtains, carpets, clothes, blankets, sheetings, table clothes, upholstery fabrics, wall coverings, artificial hair, interior materials for automobiles, outdoor reinforcing materials, and safety nets.
With respect to hair products such as wigs, hair wigs, extensions, hair bands, and doll hair, it is conventional to use human hair or artificial hair (modacrylic fibers, polyvinyl chloride fibers) or the like. However, because it has now become difficult to obtain human hair, artificial hair has become more important. Artificial hair is often made of modacrylic fibers because of their flame retardance, but they have insufficient heat resistance.
In recent years there has been proposed, as a main component for artificial hair, a polyester typified by polyethylene terephthalate which has excellent heat resistance. However, when using a polyester as an artificial hair material it has become necessary to add a flame-retardant property in view of safety. Since conventional polyester fibers are flammable, various attempts have been made to improve the flame resistance of polyester fibers. Known examples include using a fiber made of a polyester obtained by copolymerizing a flame retardant monomer containing a phosphorus atom. Known examples also include adding a flame retardant to a polyester fiber.
Several methods have been proposed which involve copolymerizing a flame retardant monomer. Copolymerizing a phosphorus compound with excellent heat stability having a phosphorus atom as a ring member is disclosed in Japanese Patent Publication No. 55-41610, copolymerizing carboxyphosphinic acid is disclosed in Japanese Patent Publication No. 53-13479, and copolymerizing or adding a phosphorus compound to a polyester containing a polyarylate is disclosed in Japanese Laid-open Patent No. 11-124732. As artificial hair to which flame retardant technology is applied, a polyester fiber copolymerized with a phosphorus compound has been proposed in Japanese Laid-open Patent No. 03-27105, for example. However, since artificial hair is required to be highly flame resistant, the copolymer polyester fiber used for artificial hair must have a high copolymerization amount. This results in a significant decrease in heat resistance of the polyester, and causes other problems which make it difficult to perform melt spinning. Also, when exposed to a flame, the artificial hair does not catch fire and burn, but becomes molten and drips.
With respect to a method which involves adding a flame retardant, it has been proposed to add a halogenated cycloalkane compound as fine particles to a polyester fiber, as disclosed in Japanese Patent Publication No. 03-57990, or add a bromine-containing alkylcyclohexane to a polyester fiber, as disclosed in Japanese Patent Publication No. 01-24913. However, in the method which involves adding a flame retardant to a polyester fiber, in order to achieve sufficient flame retardancy the addition treatment temperature must be as high as 150° C. or more, the addition treatment time must be long, or a large amount of a flame retardant must be used. This causes problems such as deteriorated fiber properties, reduced productivity and an increased production cost.
As described above, artificial hair fiber which maintains fiber properties possessed by a conventional polyester fiber such as heat resistance, strength and elongation and the like, and also has excellent setting properties and flame retardance, has not yet been produced.